Motor driver device and semiconductor device

ABSTRACT

A motor driver device includes: a detector that detects a polarity inversion timing of a current flowing through a coil of a predetermined phase of a motor; a drive control signal generator that generates a pulse-width-modulated or pulse-density-modulated drive control signal for each phase based on the detection result; and a drive voltage supply that supplies a drive voltage corresponding to the drive control signal to a corresponding coil, wherein the drive control signal generator includes a prediction processor configured to set a detection prediction interval based on two or more previously detected polarity inversion timings, and executes a frequency variable control to set a variable target frequency to be higher in the detection prediction interval than outside the detection prediction interval, the variable target frequency being a frequency of the pulse-width-modulated drive control signal or a reciprocal of a minimum pulse width of the pulse-density-modulated drive control signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-154165, filed on Aug. 20, 2018, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a motor driver device and asemiconductor device.

BACKGROUND

In a motor such as a brushless DC motor that does not have a brush-basedcommutation mechanism, it is necessary to switch the direction of acurrent supplied to a coil according to the position of a rotor. Widelyknown driving systems of a brushless DC motor include a system that usesrotor position information obtained from a Hall element and a sensorlesssystem to estimate the position of a rotor based on a zero-cross pointof a counter electromotive force (induced voltage) generated in a coilwithout using a Hall element.

Widely used control methods of a three-phase brushless motor include a120-degree conduction system (rectangular wave drive) and a 180-degreeconduction system (sinusoidal wave drive). The 120-degree conductionsystem has an advantage of relative ease of control, while the180-degree conduction system has an advantage of relatively goodcharacteristics in terms of silence and vibration.

In the sensorless system, in order to detect the counter electromotiveforce, it is necessary to make a current flow through the coil zero. Inthe 120-degree conduction system, since a non-conduction interval is setfor a coil of each phase, it is possible to easily detect the counterelectromotive force by using the set non-conduction interval. On theother hand, in the 180-degree conduction system, since a current alwaysflows in each coil, the non-conduction interval cannot be used as in the120-degree conduction system. Therefore, in the 180-degree conductionsystem employs, a method can be used to set a window interval includinga time at which a zero-cross point of the counter electromotive forceoccurs and to forcibly set the output of a driver to a high impedancestate in the window interval. However, the setting of the windowinterval may impair the silence characteristic or the like, which is aninherent advantage of the 180-degree conduction system.

Taking this into consideration, there has been proposed a system thatdoes not require the output of the driver to be forced to a highimpedance state (hereinafter referred to as a windowless system for thesake of convenience). In the windowless system, at least the terminalvoltage of a coil is used to detect a polarity inversion timing of acurrent flowing through the coil (a timing at which the direction ofcurrent flow is inverted). By periodically detecting (sampling) thepolarity of the current, it is possible to acquire phase information ofthe current and generate a drive control signal, which ispulse-width-modulated based on the acquired phase information. Then, themotor can be sensorlessly driven by supplying a drive voltage having aduty based on the drive control signal to the coil of each phase.

A sampling frequency for the current polarity detection in theabove-described windowless system depends on a PWM frequency, which isthe frequency of the drive control signal in principle. That is to say,as the PWM frequency is changed, the sampling frequency is changedaccordingly. Therefore, although increasing the PWM frequency increasesthe sampling frequency and increases the resolution of the currentpolarity detection, simply increasing the PWM frequency causes adecrease in the resolution of the drive control signal.

This will be described with reference to FIG. 18. Now, for the purposeof substantiation of the description, it is assumed that a drive controlsignal is generated based on a 20 MHz reference clock. In this case, thepulse width of the drive control signal varies with 50 ns (nanoseconds),which is the reciprocal of 20 MHz, as the minimum adjustment unit. Atthis time, a case where the PWM frequency is 100 kHz is compared with acase where the PWM frequency is 1 MHz. Since the reciprocal of 100 kHzis 10 μs (microseconds), when the PWM frequency is 100 kHz, theadjustment resolution of the pulse width of the drive control signal is“50 ns/10 μs=0.5%.” On the other hand, since the reciprocal of 1 MHz is1 μs (microsecond), when the PWM frequency is 1 MHz, the adjustmentresolution of the pulse width of the drive control signal is “50 ns/1μs=5%.”

As such, simply increasing the PWM frequency to increase the resolutionof the current polarity detection causes a decrease in the resolution ofthe drive control signal. The decrease in the resolution of the drivecontrol signal leads to an increase in torque ripple of the motor.Therefore, it is desired to suggest a system that enhances theresolution of the current polarity detection (in other words, thedetection resolution of the polarity inversion timing) while suppressingthe decrease in the resolution of the drive control signal. Although thebackground art has been described on the assumption that the pulse widthmodulation is used to generate a drive control signal, similarcircumstances exist when pulse density modulation is used to generate adrive control signal.

SUMMARY

Some embodiments of the present disclosure provide a motor driver deviceand a semiconductor device which contribute to improvement in resolutionof current polarity detection (in other words, detection resolution ofpolarity inversion timing) while suppressing a decrease in resolution ofa drive control signal.

A first aspect of the present disclosure provides a motor driver devicethat switchingly drives a brushless direct current (DC) motor havingcoils of a plurality of phases. The motor driver device includes: adetector configured to detect a polarity inversion timing of a currentflowing through a coil of a predetermined phase based on a terminalvoltage generated at one end of the coil of the predetermined phase; adrive control signal generator configured to generate apulse-width-modulated or pulse-density-modulated drive control signalfor each of the phases based on the detection result of the detector;and a drive voltage supply configured to supply a drive voltage, whichcorresponds to the drive control signal for each of the phases, to acorresponding one of the coils, wherein the drive control signalgenerator includes a prediction processor configured to set a detectionprediction interval based on two or more previously detected polarityinversion timings, and executes a frequency variable control to set avariable target frequency to be higher in the detection predictioninterval than outside the detection prediction interval, the variabletarget frequency being a frequency of the pulse-width-modulated drivecontrol signal or a reciprocal of a minimum pulse width of thepulse-density-modulated drive control signal.

In some embodiments, in the frequency variable control, the drivecontrol signal generator may set the variable target frequency to apredetermined first frequency outside the detection prediction interval,and set the variable target frequency to a predetermined secondfrequency higher than the first frequency in the detection predictioninterval. Upon detecting the polarity inversion timing after a start ofthe detection prediction interval, the drive control signal generatormay return the variable target frequency from the second frequency tothe first frequency in response to the detection of the polarityinversion timing.

In some embodiments, when the detection prediction interval ends withoutdetecting the polarity inversion timing after the start of the detectionprediction interval, the drive control signal generator may return thevariable target frequency from the second frequency to the firstfrequency in response to the end of the detection prediction interval.

In some embodiments, when the polarity inversion timing is detectedafter the detection prediction interval is set and before the setdetection prediction interval is started, the drive control signalgenerator may maintain the variable target frequency at the firstfrequency for the detection prediction interval.

In some embodiments, the drive voltage supply may generate, as the drivevoltage for each of the phases, a voltage including a pulse trainaccording to the drive control signal and a predetermined dead timeinserted into the pulse train, and the detector may detect the polarityinversion timing based on a relationship between a pulse width of theterminal voltage generated by the drive voltage at the one end of thepredetermined coil of the predetermined phase and a pulse width of thedrive control signal generated for the predetermined phase.

In some embodiments, for each of the phases, the drive voltage supplymay include a half bridge circuit including a high side transistor and alow side transistor connected to each other in series, and supply thedrive voltage to the corresponding one of the coils from a connectionnode between the high side transistor and the low side transistor. Foreach of the phases, both of the high side transistor and the low sidetransistor may be turned off in the dead time.

In some embodiments, for each of the phases, the drive voltage supplymay include a half bridge circuit including a high side transistor and alow side transistor connected to each other in series, and supply thedrive voltage to the corresponding one of the coils from a connectionnode between the high side transistor and the low side transistor. Atleast for the predetermined phase, the motor driver device may furtherinclude: a high side off detection circuit configured to detect whetheror not the high side transistor is in an off state; a low side offdetection circuit configured to detect whether or not the low sidetransistor is in an off state; and a voltage comparison circuitconfigured to compare a voltage at the connection node between the highside transistor and the low side transistor with a predeterminedvoltage. The detector may detect the polarity inversion timing based onthe detection result of the high side off detection circuit, thedetection result of the low side off detection circuit, and thecomparison result of the voltage comparison circuit.

In some embodiments, the prediction processor may predict a timing atwhich a polarity inversion timing before being detected arrives based onthe two or more previously detected polarity inversion timings, and setan interval including the predicted timing as the detection predictioninterval.

In some embodiments, the motor driver device may switchingly drive aspindle motor that rotates a magnetic disk of a magnetic disk drive asthe brushless DC motor.

A second aspect of the present disclosure provides a semiconductordevice that forms the motor driver device of the first aspect, whereinthe motor driver device is formed using an integrated circuit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration view of a mechanism of a hard diskdrive device according to an embodiment of the present disclosure.

FIG. 2 is a schematic electrical block diagram of the hard disk drivedevice according to the embodiment of the present disclosure.

FIG. 3 is an external perspective view of a driver IC mounted on thehard disk drive device according to the embodiment of the presentdisclosure.

FIG. 4 is a configuration view of an SPM and an SPM driver according toan embodiment of the present disclosure.

FIG. 5 is a functional block diagram related to generation of a drivecontrol signal in a drive control signal generation circuit.

FIG. 6 is a schematic waveform diagram of a before-modulation signal anda drive control signal regarding a U phase.

FIG. 7 is a waveform diagram of several signals and voltages involved inthe SPM driver.

FIGS. 8A and 8B are views showing a flow of a coil current in a deadtime interval.

FIG. 9 is diagram showing a relationship among a plurality of polarityinversion timings.

FIGS. 10A and 10B are explanatory views of a polarity inversionprediction timing and a detection prediction interval according to afirst example of the present disclosure.

FIG. 11 is an explanatory view of frequency variable control accordingto the first example of the present disclosure.

FIG. 12 is an operation explanatory view of a first case related to wavenumber variable control according to the first example of the presentdisclosure.

FIG. 13 is an operation explanatory view of a second case related towave number variable control according to the first example of thepresent disclosure.

FIG. 14 is an operation explanatory view of a third case related to wavenumber variable control according to the first example of the presentdisclosure.

FIG. 15 is a functional block diagram related to generation of a drivecontrol signal in a drive control signal generation circuit according toa second example of the present disclosure.

FIG. 16 is a schematic waveform diagram of a before-modulation signaland a drive control signal regarding a U phase according to the secondexample of the present disclosure.

FIG. 17 is a configuration view of a U-phase half bridge circuit and aperipheral circuit according to a third example of the presentdisclosure.

FIG. 18 is a table showing a relationship among a PWM frequency, acurrent polarity detection resolution, and a drive control signalresolution according to a related art.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be now described in detailwith reference to the drawings. Throughout the drawings, the same partsare denoted by the same reference numerals and explanation thereof willnot be repeated in principle. In the present disclosure, for the purposeof simplification of description, by denoting information, signals,physical quantities, members, and the like with reference symbols ormarks, the names of information, signals, physical quantities, members,and the like corresponding to the symbols or marks may be omitted orabbreviated. For example, a high side transistor referred to by “TrH”described later may be described as a high side transistor TrH orabbreviated as a transistor TrH, but they all refer to the same thing.

First, several terms used in the present embodiment will be described.In the present embodiment, a level refers to the level of a potentialand a high level of any signal or voltage has a potential higher than alow level thereof. A ground refers to a conductive portion having areference potential of 0 V (zero volt) or refers to the referencepotential itself. In the present embodiment, a voltage shown withoutproviding any reference represents a potential seen from the ground. Forany transistor configured as a field effect transistor (FET) includingtransistors TrH and TrL described later, an on state indicates that adrain and a source of the corresponding transistor are in a conductingstate, and an off state indicates that the drain and the source of thecorresponding transistor are in a non-conducting state (cut-off state).The on state and the off state may be expressed simply as on and off. Inany signal or voltage, switching from a low level to a high level isreferred to as up-edge, and a timing of switching from the low level tothe high level is referred to as an up-edge timing. Similarly, in anysignal or voltage, switching from a high level to a low level isreferred to as a down-edge, and a timing of switching from the highlevel to the low level is referred to as a down-edge timing. For anysignal or voltage having a level periodically switching between a lowlevel and a high level, a ratio of a length of an interval in which thesignal or voltage is at a high level to a length of an interval of onecycle of the signal or voltage is called a duty.

FIG. 1 is a schematic configuration view of a mechanism of a hard diskdrive device (hereinafter referred to as an HDD device) 1 as a magneticdisk drive device according to an embodiment of the present disclosure.

The HDD device 1 includes a magnetic disk 10 which is a recordingmedium, a magnetic head 11 (hereinafter also referred to as a head 11)that writes and reads information in and from the magnetic disk 10, anarm 12 that movably supports the magnetic head 11 in the radialdirection of the magnetic disk 10, a spindle motor 13 (hereinafter alsoreferred to as an SPM 13) that supports and rotates the magnetic disk10, and a voice coil motor 14 (hereinafter also referred to as a VCM 14)that moves and positions the magnetic head 11 in the radial direction ofthe magnetic disk 10 by rotationally driving and positioning the arm 12.

The HDD device 1 further includes a pair of piezoelectric elements 15, aload beam 16, and a ramp 17 where the magnetic head 11 is held at apredetermined retracted position spaced from the magnetic disk 10. Theload beam 16 may be attached to the tip end of the arm 12, and themagnetic head 11 may be attached to the tip end of the load beam 16. Ata tip end portion of the arm 12, the pair of piezoelectric elements 15is disposed near a mounting portion of the load beam 16. By applyingvoltages of opposite phases to the pair of piezoelectric elements 15,the pair of piezoelectric elements 15 expands and contracts in oppositephases so as to displace the magnetic head 11 at the tip end of the loadbeam 16 in the radial direction of the magnetic disk 10.

As described above, the HDD device 1 adopts a so-called two-stageactuator system. The VCM 14 functions as a coarse movement actuator forpositioning the magnetic head 11 coarsely (positioning the magnetic head11 with relatively coarse resolution) over the magnetic disk 10 bydriving the arm 12, and the pair of piezoelectric elements 15 functionsas a fine movement actuator for positioning the magnetic head 11precisely (positioning the magnetic head 11 with finer resolution thanthe VCM 14) over the magnetic disk 10 by adjusting the position of themagnetic head 11 based on the position of the arm 12. Hereinafter, anactuator including the pair of piezoelectric elements 15 is referred toas a microactuator (MA) 15.

The magnetic disk 10, the magnetic head 11, the arm 12 to which the MA15 and the load beam 16 are attached, the SPM 13, the VCM 14, and theramp 17 are housed in a housing of the HDD device 1. Further, themovement and displacement of the magnetic head 11 by the VCM 14 or theMA 15 in the radial direction of the magnetic disk 10 means movement anddisplacement of the magnetic head 11 in a direction connecting thecircumference and the center of the magnetic disk 10 having a diskshape. However, the movement and displacement of the magnetic head 11 bythe VCM 14 or the MA 15 may include components of movement anddisplacement in other directions (e.g., a tangential direction of thecircumference of the magnetic disk 10) in addition to the movement anddisplacement in the radial direction of the magnetic disk 10.

FIG. 2 is a schematic electrical block diagram of the HDD device 1. TheHDD device 1 is provided with a driver IC 30, a signal processingcircuit 21, a micro-processing unit (MPU) 22, and a power supply circuit23 as electrical components. The power supply circuit 23 supplies powersupply voltages for driving the driver IC 30, the signal processingcircuit 21, and the MPU 22. The MPU 22 is connected to each of thesignal processing circuit 21 and the driver IC 30 to enablebi-directional communication.

The signal processing circuit 21 outputs a recording signal for writinginformation in the magnetic disk 10 to the magnetic head 11, performssignal processing required for a signal read from the magnetic disk 10when reading the information from the magnetic disk 10, and sends asignal obtained by the signal processing to the MPU 22. The MPU 22controls the write operation and the read operation of information bythe magnetic head 11 through control of the signal processing circuit21.

The driver IC 30 is an electronic component (driver device) formed bysealing a semiconductor integrated circuit in a housing (package) madeof resin, as shown in FIG. 3. The number of pins (the number of externalterminals) of the driver IC 30 shown in FIG. 3 is merely an example. Thedriver IC 30 is provided with an SPM driver 33 for driving andcontrolling the SPM 13, a VCM driver 34 for driving and controlling theVCM 14, and an MA driver 35 for driving and controlling the MA 15. Thedriver IC 30 is further provided with an IF circuit (interface circuit)32 for enabling bi-directional communication between the MPU 22 and thedriver IC 30, and a control circuit 31 for controlling the operations ofthe drivers 33 to 35 based on control data received from the MPU 22through the IF circuit 32.

The MPU 22 performs rotation control of the magnetic disk 10 through thedrive control of the SPM 13 by controlling the SPM driver 33 of thedriver IC 30, and performs movement control and positioning of themagnetic head 11 through the drive control of the VCM 14 and the MA 15by controlling the VCM driver 34 and the MA driver 35 of the driver IC30. Position information indicating each position on the magnetic disk10 is recorded at each location of the magnetic disk 10. When themagnetic head 11 is positioned over the magnetic disk 10, this positioninformation is read by the magnetic head 11 and is transmitted to theMPU 22 through the signal processing circuit 21. The MPU 22 can controlthe VCM driver 34 and the MA driver 35 based on the positioninformation. Through this control, the VCM driver 34 supplies anecessary driving current to the VCM 14 to realize positioning of afirst stage of the magnetic head 11 and the MA driver 35 supplies anecessary voltage to the MA 15 to realize positioning of a second stageof the magnetic head 11. Note that the location of the magnetic head 11over the magnetic disk 10 means that the magnetic head 11 is locatedabove the magnetic disk 10 with a minute space between the magnetic disk10 and the magnetic head 11.

In a state where the position information is not read by the magnetichead 11, such as when the magnetic head 11 is located outside thecircumference of the magnetic disk 10, the MPU 22 can control the VCMdriver 34 and the MA driver 35 without relying on the positioninformation. For example, when moving the magnetic head 11 over themagnetic disk 10 from a retracted position in the ramp 17, the MPU 22may output to the driver IC 30 a signal instructing supply of apredetermined driving current suitable for the movement to the VCM 14.Thus, the VCM driver 34 supplies a predetermined driving current to theVCM 14 based on the signal. In the state where the position informationis not read by the magnetic head 11, since precise position control ofthe magnetic head 11 is not necessary, the supply voltage to the pair ofpiezoelectric elements 15 may be zero or a fixed voltage.

FIG. 4 shows the internal configuration of the SPM 13 and the SPM driver33 and their connection relationship. The external terminals provided inthe driver IC 30 include terminals OUTu, OUTv, and OUTw. The SPM 13 is athree-phase brushless DC motor including a star-connected U-phase coil13 u, a V-phase coil 13 v, and a W-phase coil 13 w. The SPM 13 has astator and a rotor provided with a permanent magnet, and the stator isprovided with the coils 13 u, 13 v, and 13 w. One end of the coil 13 u,one end of the coil 13 v, and one end of the coil 13 w are respectivelyconnected to the external terminals OUTu, OUTv, and OUTw, and the otherends of the coils 13 u, 13 v, and 13 w are connected in common to aneutral point 13 n. The external terminals OUTu, OUTv, and OUTw may alsobe referred to as output terminals. In the description below, whensimply written as a rotor, it refers to the rotor of the SPM 13.

The SPM driver 33 includes a U-phase half bridge circuit 50 u, a V-phasehalf bridge circuit 50 v, a W-phase half bridge circuit 50 w, apre-driver circuit 51, a drive control signal generation circuit 52, anda current polarity detection circuit 53, and drives the SPM 13sensorlessly in a windowless method. The SPM driver 33 may also drivethe SPM 13 by a 180-degree conduction method (sinusoidal wave drive).

Each of the half bridge circuits 50 u, 50 v, and 50 w includes a highside transistor TrH and a low side transistor TrL connected in seriesbetween a line to which a power supply voltage VPWR is applied and theground. The transistors TrH and TrL are configured as N-channel metaloxide semiconductor field effect transistors (MOSFETs). The power supplyvoltage VPWR is a predetermined positive DC voltage, which is 12 V(volt) as an example here.

More specifically, in each of the half bridge circuits 50 u, 50 v, and50 w, the drain of the transistor TrH is connected to a first powersupply terminal to which the power supply voltage VPWR is applied, andreceives the supply of power supply voltage VPWR. The source of thetransistor TrH and the drain of the transistor TrL are connected incommon to a node ND. The source of the transistor TrL is connected tothe ground functioning as a second power supply terminal. The nodes NDin the half bridge circuits 50 u, 50 v, and 50 w are connected to theoutput terminals OUTu, OUTv, and OUTw, respectively. Therefore, thenodes ND in the half bridge circuits 50 u, 50 v, and 50 w arerespectively connected to the one ends of the coils 13 u, 13 v, and 13 wvia the output terminals OUTu, OUTv, and OUTw, respectively. Voltagesapplied to the output terminals OUTu, OUTv, and OUTw, which correspondrespectively to the voltages at the one ends of the coils 13 u, 13 v,and 13 w, are represented by Vu, Vv, and Vw, respectively. The voltagesVu, Vv, and Vw are respectively supplied to the coils 13 u, 13 v, and 13w as drive voltages for U-phase, V-phase, and W-phase by the pre-drivercircuit 51 and the half bridge circuits 50 u, 50 v, and 50 w.

In order to realize the sensorless driving of the SPM 13, the currentpolarity detection circuit 53 performs at least one of a U-phasepolarity detection process for detecting the polarity of a currentflowing through the coil 13 u based on the voltage Vu, a V-phasepolarity detection process for detecting the polarity of a currentflowing through the coil 13 v based on the voltage Vv, and a W-phasepolarity detection process for detecting the polarity of a currentflowing through the coil 13 w based on the voltage Vw. The detectionresult by the polarity detection process is sent to the drive controlsignal generation circuit 52 as a polarity detection signal Sa.

The currents flowing through the output terminals OUTu, OUTv, and OUTwto the coils 13 u, 13 v, and 13 w are referred to as coil currents,which are respectively denoted by Iu, Iv, and Iw. Regarding the coilcurrent Iu, the polarity of the coil current Iu flowing from the node NDof the half bridge circuit 50 u to the coil 13 u via the output terminalOUTu is defined as positive, and the opposite polarity is defined asnegative. The polarities of the coil currents Iv and Iw are similarlydefined. The positive direction of a coil current is also referred to asa source direction, and the negative direction of the coil current isalso referred to as a sink direction.

Although FIG. 4 shows the state where the output terminals OUTu, OUTv,and OUTw are connected to the current polarity detection circuit 53,only one or two of the output terminals may be connected to the currentpolarity detection circuit 53. For example, when only the U-phasepolarity detection process is executed by the current polarity detectioncircuit 53, it is sufficient to connect only the output terminal OUTuamong the output terminals OUTu, OUTv, and OUTw to the current polaritydetection circuit 53.

The drive control signal generation circuit 52 generates and outputs adrive control signal DRVu for the half bridge circuit 50 u, a drivecontrol signal DRVv for the half bridge circuit 50 v, and a drivecontrol signal DRVw for the half bridge circuit 50 w based on thepolarity detection signal Sa containing phase information of a coilcurrent (in other words, positional information of the rotor). A torquecommand signal Trq* specifying a torque to be generated by the SPM 13 issupplied to the drive control signal generation circuit 52, and thedrive control signal generation circuit 52 generates the drive controlsignals DRVu, DRVv, and DRVw so that the torque specified by the torquecommand signal Trq* is generated in the SPM 13. At this time, the drivecontrol signals DRVu, DRVv, and DRVw may be generated so that sinusoidalcurrents flow in the coils 13 u, 13 v, and 13 w by referring topredetermined waveform data. Each of the drive control signals DRVu,DRVv, and DRVw is a binary signal having a variable pulse width, andtakes a high level or a low level. A control pulse width signal Sb sentfrom the drive control signal generation circuit 52 to the currentpolarity detection circuit 53, and a prediction processor 54 and afrequency controller 55 contained in the drive control signal generationcircuit 52 will be described later.

The pre-driver circuit 51 controls the state of each half bridge circuitby controlling the gate potential of each of the transistors in the halfbridge circuits 50 u, 50 v, and 50 w according to the drive controlsignals DRVu, DRVv, and DRVw. Thereby, voltages obtained by switchingthe power supply voltage VPWR according to the drive control signalsDRVu, DRVv, and DRVw are applied as the drive voltages Vu, Vv, and Vw tothe output terminals OUTu, OUTv, and OUTw, respectively, to switchinglydrive the SPM 13. In a target half bridge circuit which is any one ofthe half bridge circuits 50 u, 50 v, and 50 w, a state where thetransistor TrH is turned on and the transistor TrL is turned off isreferred to as an output high state, and a state where the transistorTrH is turned off and the transistor TrL is turned on is referred to asan output low state. Assuming that the on resistances of the transistorsTrH and TrL are zero, for example, when the half bridge circuit 50 u isin the output high state, the power supply voltage VPWR is applied tothe output terminal OUTu via the high side transistor TrH. When the halfbridge circuit 50 u is in the output low state, the ground potential isapplied to the output terminal OUTu via the low side transistor TrL(here, the transient state is ignored). The same applies to the halfbridge circuits 50 v and 50 w.

Now, a detailed operation of the SPM driver 33 will be described bytaking, as an example, a case where the drive control signal generationcircuit 52 generates pulse width-modulated signals as the drive controlsignals DRVu, DRVv, and DRVw. Here, it is assumed that the U-phasepolarity detection processing is performed by the current polaritydetection circuit 53.

FIG. 5 is a functional block diagram related to generation of a drivecontrol signal in the drive control signal generation circuit 52. Thedrive control signal generation circuit 52 generates before-modulationsignals Vuc, Vvc, and Vwc based on the polarity detection signal Sa, thetorque command signal Trq*, and the predetermined waveform data, andgenerates the drive control signals DRVu, DRVv, and DRVw by performingpulse width modulation on the before-modulation signals Vuc, Vvc, andVwc. The before-modulation signals Vuc, Vvc, and Vwc indicate voltagesto be applied to the output terminals OUTu, OUTv, and OUTw,respectively, in order to flow sinusoidal coil currents Iu, Iv, and Iw,and have an amplitude corresponding to the signal Trq*.

FIG. 6 shows schematic waveforms of the before-modulation signal Vuc andthe pulse-width-modulated drive control signal DRVu. The drive controlsignal DRVu is a pulse width modulation signal having a predeterminedPWM frequency, and is a binary signal having a cycle, which is thereciprocal of the PWM frequency. The same applies to the drive controlsignals DRVv and DRVw.

The pre-driver circuit 51 generates the drive voltages Vu, Vv, and Vw,which are pulse trains having duties according to the drive controlsignals DRVu, DRVv, and DRVw, respectively, and into each of which apredetermined dead time T_(D) is inserted. The pre-driver circuit 51supplies the generated drive voltages Vu, Vv, and Vw to the outputterminals OUTu, OUTv, and OUTw (i.e., the one ends of the coils 13 u, 13v, and 13 w). In each phase, in the dead time T_(D) (in a dead timeinterval having a time length corresponding to the dead time T_(D)),both of the transistors TrH and TrL are turned off.

FIG. 7 shows waveforms of the drive control signal DRVu, gate signalsV_(GH) and V_(GL) supplied to the gates of the transistors TrH and TrLof the U-phase half bridge circuit 50 u, and the drive voltage Vu. Inthis embodiment, in each cycle of the drive control signal DRVu, it isassumed that the gate signal V_(GH) has a high level for a time shorterby the dead time T_(D) than the time when the drive control signal DRVuhas a high level, and the gate signal V_(GL) has a high level for a timeshorter by the dead time T_(D) than the time when the drive controlsignal DRVu has a low level. The U-phase half bridge circuit 50 u is inthe output high state when the gate signal V_(GH) is at the high level,and is in the output low state when the gate signal V_(GL) is at thehigh level.

The description will be given starting from an output low interval inwhich the drive control signal DRVu and the gate signal V_(GH) are atthe low level and the gate signal V_(GL) is at the high level. Thetransistors TrH and TrL are in the off state and the on state,respectively, in the output low interval. When an up-edge occurs in thedrive control signal DRVu starting from the output low interval, theoutput low interval transits to a first dead time interval. In the firstdead time interval, the drive control signal DRVu is at the high level,and the gate signal V_(GL) has the low level in response thereto, butthe gate signal V_(GH) remains at the low level. When the dead timeT_(D) elapses from the start of the first dead time interval, the firstdead time interval shifts to an output high interval in which the drivecontrol signal DRVu and the gate signal V_(GH) are at the high level andthe gate signal V_(GL) is at the low level. The transistors TrH and TrLare in the on state and the off state, respectively, in the output highinterval. Thereafter, when a down-edge occurs in the drive controlsignal DRVu, the output high interval transits to a second dead timeinterval. In the second dead time interval, the drive control signalDRVu is at the low level, and the gate signal V_(GH) has the low levelin response thereto, but the gate signal V_(GL) remains at the lowlevel. When the dead time T_(D) elapses from the start of the seconddead time interval, the second dead time interval shifts to an outputlow interval. In this manner, the output low interval, the first deadtime interval, the output high interval, and the second dead timeinterval are repeatedly traversed in this order. The time length of eachof the first and second dead time intervals coincides with thepredetermined dead time T_(D), and the transistors TrH and TrL are bothturned off in the first and second dead time intervals.

A time Ta represents the pulse width of the drive control signal DRVuand is equal to the time when the drive control signal DRVu goes to thehigh level in each cycle of the drive control signal DRVu. On the otherhand, a time Tb represents the pulse width of the voltage Vu and isequal to the time when the voltage Vu goes to the high level in eachcycle of the voltage Vu (the time when the voltage Vu is equal to orhigher than a predetermined threshold voltage). Here, as shown in FIG.8A, when the polarity of the coil current Iu is positive, since acurrent flows from the half bridge circuit 50 u to the coil 13 u througha parasitic diode of the transistor TrL of the half bridge circuit 50 uin each dead time period (i.e., since a current flows in the sourcedirection), the terminal voltage Vu at one end of the coil 13 u becomeslower by the forward voltage of the parasitic diode than 0 V. As aresult, the time Tb is shorter than the time Ta. On the other hand, asshown in FIG. 8B, when the polarity of the coil current Iu is negative,since the coil current Iu flows from the coil 13 u to the half bridgecircuit 50 u in each dead time interval and flows through the parasiticdiode of the transistor TrH to the terminal to which the power supplyvoltage VPWR is applied (i.e., since a current flows in the sinkdirection), the terminal voltage Vu at the one end of the coil 13 ubecomes higher by the forward voltage of the parasitic diode than thepower supply voltage VPWR. As a result, the time Tb is longer than thetime Ta.

Using the above-described characteristics, the polarity of the coilcurrent Iu can be detected by comparing the pulse width (i.e., the timeTa) of the drive control signal DRVu with the pulse width (i.e., thetime Tb) of the voltage Vu. Specifically, the current polarity detectioncircuit 53 performs the above comparison. When “Tb<Ta,” the currentpolarity detection circuit 53 determines that the polarity of the coilcurrent Iu is positive, and outputs the polarity detection signal Sa ofa high level. When “Tb>Ta,” the current polarity detection circuit 53determines that the polarity of the coil current Iu is negative, andoutputs the polarity detection signal Sa of a low level.

As the pulse width of the drive control signal DRVu and the pulse widthof the voltage Vu, a time Tc when the drive control signal DRVu is atthe low level and a time Td when the voltage Vu is at the low level maybe used to detect the polarity of the coil current Iu. A signalindicating the pulse width (the time Ta or Tc) of the drive controlsignal DRVu is sent as the control pulse width signal Sb from the drivecontrol signal generation circuit 52 to the current polarity detectioncircuit 53 (see FIG. 4). The current polarity detection circuit 53recognizes the pulse width of the drive control signal DRVu based on thesignal Sb. The current polarity detection circuit 53 can obtain the timeTb or Td using a comparator that compares the voltage Vu with apredetermined threshold voltage (a voltage of 0 V or more and the powersupply voltage VPWR or less, for example, 1 V).

The switching of the level of the polarity detection signal Sarepresents a timing at which the polarity of the coil current Iu isinverted (hereinafter referred to as a polarity inversion timing). Thepolarity inversion timing is also a zero-cross timing at which the valueof the coil current Iu crosses zero. Since the polarity inversion of thecoil current Iu occurs every 180 degrees of the phase of the coilcurrent Iu, the polarity detection signal Sa is a signal indicating thephase of the coil current Iu. Therefore, it is possible to drive the SPM13 sensorlessly based on the polarity detection signal Sa. It can besaid that the current polarity detection circuit 53 is a circuit thatdetects the polarity inversion timing and indicates the result of thedetection at the up-edge or the down-edge of the signal Sa.

The polarity inversion timing includes a negative transition timing atwhich the polarity of the coil current Iu transitions from positive tonegative and a positive transition timing at which the polarity of thecoil current Iu transitions from negative to positive. The currentpolarity detection circuit 53 may detect both of the negative transitiontiming and the positive transition timing as the polarity inversiontiming, or may detect only one of them as the polarity inversion timing.In the following, it is assumed that only the positive transition timingis detected as the polarity inversion timing. Then, the up-edge timingof the polarity detection signal Sa is detected as the polarityinversion timing.

The detailed configuration examples, operation examples, applicationexamples, and modifications of the HDD device 1 (in particular, thedrive control signal generation circuit 52 and the current polaritydetection circuit 53) based on the above contents will be describedbelow in the first to fifth examples. In particular, unless statedotherwise or contradictory, the matters described above in the presentembodiment are applied to the first to fifth examples to be describedbelow, and with respect to matters in the first to fifth examples thatare contradictory to the above contents, the description in the first tofifth examples is given priority. Further, unless contradictory, thematters described in any of the first to fifth examples described belowcan be applied to any other examples (that is to say, two or more of thefirst to fifth examples can be used in combination).

First Example

A first example will be described. The drive control signal generationcircuit 52 is supplied with a predetermined reference clock having apredetermined clock frequency, and uses the reference clock to generatethe drive control signals DRVu, DRVv, and DRVw in a digital domain. Thatis to say, the pulse width of each drive control signal is adjusted in aunit that is reciprocal of the clock frequency. Here, for the purpose ofsubstantiation of the description, it is considered that the clockfrequency is 20 MHz (megahertz). Then, the pulse width of each drivecontrol signal varies with 50 ns (nanosecond), which is the reciprocalof 20 MHz, as the minimum adjustment unit.

On the other hand, the sampling frequency for current polarity detectionby the current polarity detection circuit 53 depends on the PWMfrequency, which is the frequency of pulse width modulation in the drivecontrol signal generation circuit 52 in principle. The PWM frequencyused herein corresponds to the frequency of the drive control signalsDRVu, DRVv, and DRVw. As described above with reference to FIG. 18, whenthe PWM frequency is increased, since the sampling frequency forpolarity detection of a current is increased, the resolution of polaritydetection of the current (in other words, detection resolution ofpolarity inversion timing) increases. However, simply increasing the PWMfrequency decreases the resolution of each drive control signal. Thedecrease in resolution of the drive control signal leads to an increasein torque ripple of the SPM 13.

Taking this into consideration, the drive control signal generationcircuit 52 according to the present embodiment performs characteristiccontrol to improve the resolution of current polarity detection whilesuppressing a decrease in resolution of a drive control signal. Thischaracteristic control will be described below.

As shown in FIG. 9, now, a polarity inversion timing coming at the i-thtime is represented by “T[i]” (where i is an integer). Then, as timeadvances, the polarity inversion timings T[1], T[2], T[3], . . . ,T[n−2], T [n−1], T[n] (where n is an integer of three or more) aresequentially traversed. In the steady state of rotation of the SPM 13,since an interval between two temporally adjacent polarity inversiontimings (hereinafter referred to as a polarity inversion interval) issubstantially constant, it is possible to predict a polarity inversiontiming that will come in the future, based on a plurality of detectedpolarity inversion timings.

The prediction processor 54 performs the above prediction. Theprediction processor 54 predicts a timing at which the next polarityinversion will occur, based on two or more detected polarity inversiontimings. More specifically, the prediction processor 54 may predict thenext polarity inversion timing before being detected, based on polarityinversion intervals for the most recent past VAL_(A) times (whereVAL_(A) is an integer of one or more) and the polarity inversion timingdetected most recently. The timing predicted here is referred to as a“polarity inversion prediction timing,” and a polarity inversionprediction timing for the i-th polarity inversion timing is representedby “T_(EST)[i].”

Typically, for example, an average value of the polarity inversionintervals for the most recent past VAL_(A) times may be obtained, and atiming after a time of the average value from the most recently detectedpolarity inversion timing may be derived as the polarity inversionprediction timing. That is to say, referring to FIG. 10A, for example,when “VAL_(A)=3,” before arrival of the polarity inversion timing T[n]after detection of the polarity inversion timings T[n−3] to T[n−1], theprediction processor 54 obtains an average value of the interval betweenthe timing T[n−3] and T[n−2] and the interval between the timing T[n−2]and T[n−1], and derives a timing after a time of the average value fromthe timing T[n−1] as the polarity inversion prediction timingT_(EST)[n].

After deriving the polarity inversion prediction timing, the predictionprocessor 54 sets a detection prediction interval centered on thepolarity inversion prediction timing and having a time width of “2×WD,”where WD is a time (time length) predetermined to be sufficientlyshorter than the polarity inversion interval. The detection predictioninterval centered on the polarity inversion prediction timing T_(EST)[i]is represented by “P_(EST)[i].” FIGS. 10A and 10B show a detectionprediction interval P_(EST)[n], and FIG. 10B is an enlarged view of thedetection prediction interval P_(EST)[n].

The frequency controller 55 can perform a frequency variable control onthe PWM frequency, which is the frequency of the drive control signalsDRVu, DRVv, and DRVw, as a variable target frequency. As shown in FIG.11, the frequency variable control refers to a control for setting thevariable target frequency (in this case, the PWM frequency) to apredetermined frequency f_(L) outside the detection prediction interval,while setting the variable target frequency to a predetermined frequencyf_(H) higher than the frequency f_(L) within the detection predictioninterval. When the reference clock is 20 MHz, for example, the frequencyf_(L) may be 150 kHz and the frequency f_(H) may be 400 kHz. Of course,the specific numerical values of the frequencies f_(L) and f_(H) can bechanged variously.

Since the actual polarity inversion timing is likely to be detectedwithin the detection prediction interval, the frequency variable controlcan substantially improve the resolution of current polarity detection.Further, since the variable target frequency is increased only in thedetection prediction interval, the decrease in resolution of the drivecontrol signal is suppressed as compared to a case where the variabletarget frequency is uniformly increased. That is to say, it is possibleto increase the resolution of current polarity detection whilesuppressing the decrease in resolution of the drive control signal.

The frequency controller 55 may operate as described below based on thefrequency variable control. That is to say, when the polarity inversiontiming is actually detected in a state where the variable targetfrequency is set to the frequency f_(H) in the detection predictioninterval, the frequency controller 55 may switch the variable targetfrequency from the frequency f_(H) to the frequency f_(L) in response tothe detection (a first case described later; see FIG. 12). In addition,when the polarity inversion timing predicted to be detected in thedetection prediction interval is detected before the detectionprediction interval is started, the frequency controller 55 may cancelthe execution of the frequency variable control for the detectionprediction interval and maintain the variable target frequency at thefrequency f_(L) in the detection prediction interval (a third casedescribed later; see FIG. 14).

Operations of the first to third cases involved in the frequencyvariable control will be described with reference to FIGS. 12 to 14. Inthe first to third cases, it is assumed that the polarity inversionprediction timing T_(EST)[n] and the detection prediction intervalP_(EST)[n] are set by the prediction processor 54, before the arrival ofthe polarity inversion timing T[n] after the detection of the polarityinversion timing T[n−1]. The start timing and the end timing of thedetection prediction interval P_(EST)[n] are represented by “T_(S)[n]”and “T_(E)[n],” respectively. The operations of the first to third caseswill be described starting from a timing 610 after the detection of thepolarity inversion timing T[n−1] and before the timing T_(S)[n]. Sincethe polarity detection signal Sa is at the low level at the timing 610and the timing 610 is a timing outside the detection predictioninterval, the variable target frequency at the timing 610 is thefrequency f_(L).

FIG. 12 is an operation explanatory view of the first case related tothe frequency variable control. In the first case, an up-edge occurs inthe polarity detection signal Sa at a timing 611 in the detectionprediction interval P_(EST)[n], and the timing 611 is detected as theactual polarity inversion timing T[n].

In the first case, the frequency controller 55 increases the variabletarget frequency from the frequency f_(L) to the frequency f_(H) at thetiming T_(S)[n] by the frequency variable control, returns the variabletarget frequency from the frequency f_(H) to the frequency f_(L) inresponse to the detection of the actual polarity inversion timing T[n]at the timing 611, and, after that, maintains the variable targetfrequency at the frequency f_(L) until the next detection predictioninterval arrives. This is because it is not necessary to increase thevariable target frequency after the actual polarity inversion timing isdetected, and the decrease in resolution of the drive control signal canbe suppressed by quickly returning the variable target frequency to thefrequency f_(L).

FIG. 13 is an operation explanatory view of the second case related tothe frequency variable control. In the second case, the polarityinversion timing T[n] does not come between the timing 610 and thetiming T_(S)[n] and does not come also in the detection predictioninterval P_(EST)[n]. An up-edge occurs in the polarity detection signalSa at a timing 612 after the end of the detection prediction intervalP_(EST)[n], and the timing 612 is detected as the actual polarityinversion timing T[n].

In the second case, the frequency controller 55 increases the variabletarget frequency from the frequency f_(L) to the frequency f_(H) at thetiming T_(S)[n] by the frequency variable control, maintains thevariable target frequency at the frequency f_(H) up to the timingT_(E)[n], and, after that, returns the variable target frequency fromthe frequency f_(H) to the frequency f_(L) at the timing T_(E)[n].Thereafter, the variable target frequency is maintained at the frequencyf_(L) until the next detection prediction interval arrives. That is tosay, after the start of the detection prediction interval P_(EST)[n],when the detection prediction interval P_(EST)[n] ends without detectingthe polarity inversion timing T[n], the frequency controller 55 returnsthe variable target frequency from the frequency f_(H) to the frequencyf_(L) in response to the end of the detection prediction interval. Theprediction may be missed and the actual polarity inversion timing maynot be detected in the detection prediction interval. However, in termsof the resolution of the drive control signal, it is not desirable tomaintain the state in which the variable target frequency is increasedfor a long time. Thus, the variable target frequency is returned to thefrequency f_(L) at the end of the detection prediction interval.

FIG. 14 is an operation explanatory view of the third case related tothe frequency variable control. In the third case, an up-edge occurs inthe polarity detection signal Sa at a timing 613 before the start timingT_(S)[n] of the detection prediction interval P_(EST)[n] after thetiming 610, and the timing 613 is detected as the actual polarityinversion timing T[n].

In the third case, the frequency controller 55 maintains the variabletarget frequency at the frequency f_(L) in the detection predictioninterval P_(EST)[n] without executing the frequency variable control onthe detection prediction interval P_(EST)[n]. This is because, it is notnecessary to increase the variable target frequency after the actualpolarity inversion timing is detected.

Second Example

A second example will be described. It has been illustrated in the firstexample that the pulse width modulation is used to generate the drivecontrol signal, but pulse density modulation may be used to generate thedrive control signal. In the second example, it is assumed that thepulse density modulation is used to generate the drive control signalsDRVu, DRVv, and DRVw. The drive control signal generation circuit 52according to the second example is configured to be able to change thefrequency in the pulse density modulation (hereinafter referred to as aPDM frequency). The pulse density modulation may be abbreviated as PDM.When the pulse density modulation is used, each of the drive controlsignals DRVu, DRVv, and DRVw is a compressional wave (one-bitcompressional wave) as a binary signal, but the reciprocal of theminimum pulse width in the compressional wave corresponds to the PDMfrequency (see FIG. 16 described later).

FIG. 15 is a functional block diagram related to generation of a drivecontrol signal in the drive control signal generation circuit 52. Thedrive control signal generation circuit 52 generates before-modulationsignals Vuc, Vvc, and Vwc based on the polarity detection signal Sa, thetorque command signal Trq*, and the predetermined waveform data, andgenerates drive control signals DRVu, DRVv, and DRVw by performing pulsedensity modulation on the before-modulation signals Vuc, Vvc, and Vwc.The before-modulation signals Vuc, Vvc, and Vwc indicate voltages to beapplied to the output terminals OUTu, OUTv, and OUTw, respectively, inorder to flow sinusoidal coil currents Iu, Iv, and Iw, and have anamplitude corresponding to the signal Trq*.

FIG. 16 shows schematic waveforms of the before-modulation signal Vucand the pulse-density-modulated drive control signal DRVu. The drivecontrol signal DRVu is a pulse density modulation signal having thereciprocal of the PDM frequency as the minimum pulse width. The sameapplies to the drive control signals DRVv and DRVw. As in the case ofusing the pulse width modulation, the drive control signal generationcircuit 52 is supplied with a predetermined reference clock having apredetermined clock frequency, and uses the reference clock to generatethe drive control signals DRVu, DRVv, and DRVw in a digital domain. Thatis to say, in the second example, the clock frequency is used as the PDMfrequency. When the clock frequency is 20 MHz (megahertz), the pulsewidth of each drive control signal varies with 50 ns (nanosecond), whichis the reciprocal of 20 MHz, as the minimum adjustment unit.

On the other hand, the sampling frequency for current polarity detectionby the current polarity detection circuit 53 depends on the PDMfrequency in principle. As in the case of using the pulse widthmodulation, when the PDM frequency is increased, since the samplingfrequency for current polarity detection is increased, the resolution ofcurrent polarity detection (in other words, detection resolution ofpolarity inversion timing) increases. However, simply increasing the PDMfrequency decreases the resolution of each drive control signal.

Therefore, in the second example, after setting the PDM frequency as thevariable target frequency, the same operation as in the first exampleincluding the above-described frequency variable control may beperformed. The method of setting the polarity inversion predictiontiming and the detection prediction interval and the operations of thefirst to third cases are common to the case of using the pulse widthmodulation and the case of using the pulse density modulation.

Third Example

A third example will be described. The method of detecting the polarityof the coil current Iu is not limited to that described above. In thethird example, another method of detecting the polarity of the coilcurrent Iu will be described. The SPM driver 33 includes a high side offsensor (high side off detection circuit) that detects whether or not thetransistor TrH is in an off state with respect to a half bridge circuitamong at least one of the U-phase, the V-phase, and the W-phase, a lowside off sensor (low side off detection circuit) that detects whether ornot the transistor TrL is in an off state, and an output sensor (voltagecomparison circuit) that compares a voltage at a connection node betweenthe transistors TrH and TrL with a predetermined voltage.

Referring to FIG. 17, it is considered here that the sensors areprovided for the U-phase half bridge circuit 50 u. That is to say, theSPM driver 33 is provided with sensors 61 to 63 as the sensors for thehalf bridge circuit 50 u. The high side off sensor 61 detects whether ornot the transistor TrH is in an off state based on the level of the gatesignal V_(GH) of the transistor TrH (that is to say, based on the gatepotential of the transistor TrH), and outputs a signal Sig61 indicatingthe detection result. The low side off sensor 62 detects whether or notthe transistor TrL is in an off state based on the level of the gatesignal V_(GL) of the transistor TrL (that is to say, based on the gatepotential of the transistor TrL), and outputs a signal Sig62 indicatingthe detection result. The output sensor 63 compares the voltage Vu atthe output terminal OUTu with a predetermined voltage, and outputs asignal Sig63 indicating the comparison result. The current polaritydetection circuit 53 according to the third example detects the polarityof the coil current Iu based on the signals Sig61 to Sig63, andgenerates and outputs a polarity detection signal Sa.

Specifically, the output sensor 63 compares the voltage Vu with apredetermined positive voltage V_(REF1) (for example, 0.5 V), which islower than the power supply voltage VPWR. When there is a timing atwhich the voltage Vu is equal to or lower than the predetermined voltageV_(REF1) while the transistor TrL is in the off state, the currentpolarity detection circuit 53 determines that the polarity of the coilcurrent Iu is positive (i.e., determines that the coil current Iu flowsin the source direction). When the transistor TrL is turned off whilethe coil current Iu is flowing in the sink direction, the voltage Vu issufficiently high. Therefore, when the voltage Vu is lower than thepredetermined voltage V_(REF1) while the transistor TrL is turned off,it is considered that the coil current Iu flows in the reverse of thesink direction, that is to say, in the source direction (see FIG. 8A).

Further, the output sensor 63 compares the voltage Vu with apredetermined positive voltage V_(REF2) (for example, 11.5 V), which islower than the power supply voltage VPWR. When there is a timing atwhich the voltage Vu is equal to or lower than the predetermined voltageV_(REF2) while the transistor TrH is in the off state, the currentpolarity detection circuit 53 determines that the polarity of the coilcurrent Iu is negative (i.e., determines that the coil current Iu flowsin the sink direction). This is because, in the state where the coilcurrent Iu flows in the sink direction, there is a timing at which thevoltage Vu is equal to or higher than the predetermined voltage V_(REF2)due to a current flow from the SPM 13 even when the transistor TrH isturned off (see FIG. 8B).

The predetermined voltages V_(REF1) and V_(REF2) may be different fromeach other, and typically, “VPWR>V_(REF2)>V_(REF1)>0”. However, it isalso possible to set the predetermined voltages V_(REF1) and V_(REF2) toa common voltage (for example, a half of the power supply voltage VPWR).

Further, the polarity of the coil current Iu and the polarity inversiontiming may be detected based on the voltage Vu when both of thetransistors TrH and TrL are in the off state.

Upon determining that the polarity of the coil current Iu is positive,the current polarity detection circuit 53 maintains (latches) thepolarity detection signal Sa at the high level until the currentpolarity detection circuit 53 determines that the polarity of the coilcurrent Iu is negative. Thereafter, when the current polarity detectioncircuit 53 determines that the polarity of the coil current Iu isnegative, the polarity detection signal Sa is switched from the highlevel to the low level, and is maintained (latched) at the low leveluntil the current polarity detection circuit 53 determines that thepolarity of the current Iu is positive next time. That is to say, whenthe current polarity detection circuit 53 determines that the polarityof the coil current Iu is positive, the polarity detection signal Sa isswitched from the low level to the high level. With such a configurationand operation, the up-edge timing or the down-edge timing of thepolarity detection signal Sa can be used as the polarity inversiontiming. However, even with such a configuration and operation,determination on whether or not the polarity of the coil current Iu isinverted can be performed only at intervals depending on the frequencyof state change of the half bridge circuit 50 u. That is to say, thesampling frequency for current polarity detection (polarity inversiondetection) depends on the PWM frequency or the PDM frequency.

Fourth Example

A fourth example will be described. Each of the above-mentionedfrequencies f_(L) and f_(H) and time WD may be variably set. That is tosay, for example, the driver IC 30 is provided with a memory (not shown)configured with a nonvolatile memory for storing various settinginformation in a nonvolatile manner. The MPU 22 can change and set firstfrequency control data, second frequency control data, and detectionprediction interval length data held in the memory by transmitting apredetermined signal to the driver IC 30.

In the SPM driver 33, a plurality of different low side frequencies areset in advance as candidates for the frequency f_(L), and the frequencycontroller 55 sets one of the plurality of low side frequencies to thefrequency f_(L) according to the first frequency control data.Similarly, in the SPM driver 33, a plurality of different high sidefrequencies are set in advance as candidates for the frequency f_(H),and the frequency controller 55 sets one of the plurality of high sidefrequencies to the frequency f_(H) according to the second frequencycontrol data. Similarly, in the SPM driver 33, a plurality of differenttimes are set in advance as candidates for the time WD, and theprediction processor 54 sets one of the plurality of times to the timeWD according to the detection prediction interval length data.

Further, the MPU 22 may instruct the driver IC 30 to invalidate theabove-described frequency variable control, and when the instruction isissued, the variable target frequency is always maintained at thefrequency f_(L).

Fifth Example

A fifth embodiment will be described.

As described above, the current polarity detection circuit 53 can detectthe polarity inversion timing (in other words, zero-cross timing) of acurrent flowing through a coil of a predetermined phase based on aterminal voltage generated at one end of the coil of the predeterminedphase. In the above description, the U-phase is particularly noted asthe predetermined phase. However, the predetermined phase may be theV-phase or the W-phase, or may be a set of two or more of the U-phase,the V-phase, and the W-phase phases.

In the half bridge circuit including the transistors TrH and TrL, thedrain of the transistor TrH is connected to the first power supplyterminal, and the source of the transistor TrL is connected to thesecond power supply terminal. The first and second power supplyterminals are arbitrary as long as they have a fixed potential. However,the potential at the first power supply terminal is higher than thepotential at the second power supply terminal. In each half bridgecircuit, a diode having a forward direction from the node ND to thefirst power supply terminal may be connected in parallel to thetransistor TrH separately from the parasitic diode of the transistorTrH, and a diode having a forward direction from the second power supplyterminal to the node ND may be connected in parallel to the transistorTrL separately from the parasitic diode of the transistor TrL.

The drive control signal generation circuit 52 generates the drivecontrol signals DRVu, DRVv, and DRVw based on the polarity detectionsignal Sa and the torque command signal Trq*. However, in a case where atorque to be generated in the SPM 13 is predetermined, the torquecommand signal Trq* may be unnecessary.

Although the example in which the SPM 13 is configured by coils of threephases has been described above, the SPM 13 may be configured by coilsof multiple phases other than three phases.

Respective components of the driver IC 30 are formed in semiconductorintegrated circuits, and a semiconductor device is constituted bysealing the semiconductor integrated circuits in a housing (package)made of resin. However, a circuit equivalent to the circuit in thedriver IC 30 may be configured using a plurality of discrete components.Alternatively, the semiconductor device may be configured by forming asingle body of the SPM driver 33 in the form of a semiconductorintegrated circuit and sealing the semiconductor integrated circuit in ahousing (package) made of resin.

In the above-described embodiment, the present disclosure is applied toa motor driver device (driver IC 30) for the SPM 13 of the HDD device 1.However, the present disclosure can be widely applied to any motordriver device that drives a motor. For example, the present disclosuremay be applied to a motor driver device for driving a fan motor for aircooling.

Each half bridge circuit may be modified in such a manner that thetransistor TrH is formed of a P-channel type MOSFET. The transistor TrLmay also be formed of a P-channel MOSFET.

Each of the transistors described above may be an arbitrary type oftransistor. For example, the transistor described above as a MOSFET maybe replaced with a junction type FET, an insulated gate bipolartransistor (IGBT), or a bipolar transistor as long as theabove-described main ideas are not impaired. The arbitrary type oftransistor has a first electrode, a second electrode, and a controlelectrode. In the FET, one and the other of the first and secondelectrodes are a drain and a source, respectively, and the controlelectrode is a gate. In the IGBT, one and the other of the first andsecond electrodes are a collector and an emitter, respectively, and thecontrol electrode is a gate. In the bipolar transistor not belonging toan IGBT, one and the other of the first and second electrodes are acollector and an emitter, respectively, and the control electrode is abase.

<<Consideration of the Present Disclosure>>

The present disclosure substantiated in the above-described embodimentsis considered.

According to one aspect of the present disclosure, a motor driver device(the driver IC 30), which switchingly drives a brushless DC motor havingcoils of a plurality of phases, includes: a detector (the currentpolarity detection circuit 53) configured to detect a polarity inversiontiming of a current flowing through a coil of a predetermined phasebased on a terminal voltage (e.g., the voltage Vu) generated at one endof the coil of the predetermined phase; a drive control signal generator(the drive control signal generation circuit 52) configured to generatea pulse-width-modulated or pulse-density-modulated drive control signalfor each of the phases based on the detection result of the detector;and a drive voltage supply (the pre-driver circuit 51 and the halfbridge circuits 50 u, 50 v, and 50 w) configured to supply a drivevoltage, which corresponds to the drive control signal for each of thephases, to a corresponding one of the coils. The drive control signalgenerator includes a prediction processor (the prediction processor 54)configured to set a detection prediction interval (the detectionprediction interval P_(EST)[n]) based on two or more detected polarityinversion timings, and executes a frequency variable control to set avariable target frequency to be higher in the detection predictioninterval than outside the detection prediction interval, the variabletarget frequency being a frequency (PWD frequency) of thepulse-width-modulated drive control signal or a reciprocal (PWMfrequency) of a minimum pulse width of the pulse-density-modulated drivecontrol signal.

Based on two or more detected polarity inversion timings, it is possibleto predict the next polarity inversion timing and set a detectionprediction interval. Further, when the variable target frequency isincreased within the detection prediction interval, the resolution ofcurrent polarity detection (in other words, the detection resolution ofpolarity inversion timing) can be enhanced. Although a decrease inresolution of the drive control signal by the increase in the variabletarget frequency is a concern, in the variable frequency control, sincethe variable target frequency is relatively lowered outside thedetection prediction interval, the decrease in resolution of the drivecontrol signal is suppressed.

According to the present disclosure in some embodiments, it is possibleto provide a motor driver device and a semiconductor device whichcontribute to improvement in resolution of current polarity detection(in other words, detection resolution of polarity inversion timing)while suppressing a decrease in resolution of a drive control signal.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the embodiments described herein maybe embodied in a variety of other forms. Furthermore, various omissions,substitutions and changes in the form of the embodiments describedherein may be made without departing from the spirit of the disclosures.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosures.

What is claimed is:
 1. A motor driver device that switchingly drives abrushless direct current (DC) motor having coils of a plurality ofphases, the motor driver device comprising: a detector configured todetect a polarity inversion timing of a current flowing through a coilof a predetermined phase based on a terminal voltage generated at oneend of the coil of the predetermined phase; a drive control signalgenerator configured to generate a pulse-width-modulated orpulse-density-modulated drive control signal for each of the phasesbased on the detection result of the detector; and a drive voltagesupply configured to supply a drive voltage, which corresponds to thedrive control signal for each of the phases, to a corresponding one ofthe coils, wherein the drive control signal generator includes aprediction processor configured to set a detection prediction intervalbased on two or more previously detected polarity inversion timings, andexecutes a frequency variable control to set a variable target frequencyto be higher in the detection prediction interval than outside thedetection prediction interval, the variable target frequency being afrequency of the pulse-width-modulated drive control signal or areciprocal of a minimum pulse width of the pulse-density-modulated drivecontrol signal.
 2. The motor driver device of claim 1, wherein, in thefrequency variable control, the drive control signal generator sets thevariable target frequency to a predetermined first frequency outside thedetection prediction interval, and sets the variable target frequency toa predetermined second frequency higher than the first frequency in thedetection prediction interval, and wherein upon detecting the polarityinversion timing after a start of the detection prediction interval, thedrive control signal generator returns the variable target frequencyfrom the second frequency to the first frequency in response to thedetection of the polarity inversion timing.
 3. The motor driver deviceof claim 2, wherein, when the detection prediction interval ends withoutdetecting the polarity inversion timing after the start of the detectionprediction interval, the drive control signal generator returns thevariable target frequency from the second frequency to the firstfrequency in response to the end of the detection prediction interval.4. The motor driver device of claim 2, wherein, when the polarityinversion timing is detected after the detection prediction interval isset and before the set detection prediction interval is started, thedrive control signal generator maintains the variable target frequencyat the first frequency for the detection prediction interval.
 5. Themotor driver device of claim 1, wherein the drive voltage supplygenerates, as the drive voltage for each of the phases, a voltageincluding a pulse train according to the drive control signal and apredetermined dead time inserted into the pulse train, and wherein thedetector detects the polarity inversion timing based on a relationshipbetween a pulse width of the terminal voltage generated by the drivevoltage at the one end of the coil of the predetermined phase and apulse width of the drive control signal generated for the predeterminedphase.
 6. The motor driver device of claim 5, wherein for each of thephases, the drive voltage supply includes a half bridge circuitincluding a high side transistor and a low side transistor connected toeach other in series, and supplies the drive voltage to thecorresponding one of the coils from a connection node between the highside transistor and the low side transistor, and wherein for each of thephases, both of the high side transistor and the low side transistor areturned off in the dead time.
 7. The motor driver device of claim 1,wherein for each of the phases, the drive voltage supply includes a halfbridge circuit including a high side transistor and a low sidetransistor connected to each other in series, and supplies the drivevoltage to the corresponding one of the coils from a connection nodebetween the high side transistor and the low side transistor, wherein atleast for the predetermined phase, the motor driver device furtherincludes: a high side off detection circuit configured to detect whetheror not the high side transistor is in an off state; a low side offdetection circuit configured to detect whether or not the low sidetransistor is in an off state; and a voltage comparison circuitconfigured to compare a voltage at the connection node between the highside transistor and the low side transistor with a predeterminedvoltage, and wherein the detector detects the polarity inversion timingbased on the detection result of the high side off detection circuit,the detection result of the low side off detection circuit, and thecomparison result of the voltage comparison circuit.
 8. The motor driverdevice of claim 1, wherein the prediction processor predicts a timing atwhich a polarity inversion timing before being detected arrives based onthe two or more previously detected polarity inversion timings, and setsan interval including the predicted timing as the detection predictioninterval.
 9. The motor driver device of claim 1, wherein the motordriver device switchingly drives a spindle motor that rotates a magneticdisk of a magnetic disk drive as the brushless DC motor.
 10. Asemiconductor device that forms the motor driver device of claim 1,wherein the motor driver device is formed using an integrated circuit.